1. Field of the Invention
The present invention relates to a system for transferring large quantities of heat without transfer of mass.
2. Description of the Prior Art
Diffusion has long been employed to separate molecules. Graham [On the law of diffusion of gases. Philosophical Magazine, Vol. 2, pp. 175-351 (1833)], who first related the molecular diffusion coefficient to the square root of molecular weight, separated gases based upon this principle in the 19th century. Hertz developed a technique based on diffusion to separate gases in a countercurrent system [Z. Physik., Vol. 19, p. 35 (1923); Z. Physik, Vol. 91, p. 810 (1934)].
This technique was extended to liquids by Lange [Z. Naturwiss., Vol. 16, p. 115 (1928); Vol. 17, p. 228 (1928)].
Dreyer et al [Die Steigerung des Diffusions-transportes durch Pulsations diffusion, Z. Naturforsch. Vol. 23, pp. 498-503 (1968); Die Bestimmung von Diffusionskoeffizienten nach der Pulsationsmethode, Z. Naturforsch. Vol. 24, pp. 883-886 (1969)] describe a system for determining the diffusion coefficients of solutes such as KCl, NaCl and CaCl.sub.2 comprising two containers connected by a capillary and a mechanism for creating pulsating oscillations in the liquid contained in the capillary. Although the authors discovered an enhancement of transport by several orders of magnitude across the capillary, they do not describe or suggest utilization of the system to separate solutes contained in a common solvent.
Modified principles of diffusion are used industrially today, especially to separate isotopes of uranium. Diffusion has been used to separate solutes in liquid solution, however, the efficacy of the process is low because the molecular diffusion coefficient of solutes in liquids is about five orders of magnitude smaller than the diffusion coefficient of gases in a gaseous phase, thus reducing the possible yield for a given configuration.
Enhanced diffusion (or dispersion) by oscillatory motion of a fluid finds its roots in the theoretical work by Watson (J. Fluid. Mech., 133, p. 233 (1983) who himself expanded on a study by Taylor on the dispersion of solutes in steady laminar flow (Proc. R. Soc. London Ser. A 219, p. 186 (1953). Kurzweg et al recently described the conditions of optimal transport in gases by proper tuning of the experimental variables (Phys. Fluids, Vol. 29, p. 1324 (1986)).
The general principle involved may be described thusly: The oscillation of a fluid column in a tube generates a large surface between the oscillating core and the boundary layer which is essentially not moving. This surface is made available for diffusion. The theory predicts that, under certain conditions, the dispersion coefficient (i.e., the effective diffusion coefficient) is proportional to the square root of oscillation frequency, to the square of the average oscillation amplitude, and to the molecular diffusion coefficient. The diffusion rate (flux) of a solute in an oscillatory system is proportional to the dispersion coefficient, and to the concentration gradient and is dependent on geometry.
U.S. Pat. No. 4,590,993 describes a device for the transport of large conduction heat flux between two locations of differing temperature which includes a pair of fluid reservoirs for positioning at the respective locations connected by at least one duct, and preferably a plurality of ducts, having walls of a material which conducts heat. A heat transfer fluid, preferably a liquid, and preferably a liquid metal such as mercury, lithium or sodium, fills both reservoirs and the connecting ducts. An oscillatory axial movement or flow of working fluid is established within the ducts, with the extent of fluid movement being less than the duct length. Preferably the oscillatory movement is sinusoidal. Heat is transferred radially between the fluid and the duct walls and thence axially along the ducts. The rate of heat transfer is greatly enhanced by a physical mechanism which may be described as a high time-dependent radial temperature gradient produced by fluid oscillations. During most of each sinusoidal cycle, fluid in the wall-near region has a temperature different from the core of the fluid column, with most of the temperature difference concentrated across a relatively thin boundary layer.
U.S. Pat. No. 3,891,0289 describes a regenerative heat-exchanger involving the use of a reciprocating piston containing holes to transfer the heat contained in hot exhaust gases of a combustion engine to the air taken in.
It is an object of the present invention to provide a heat-transfer system wherein the heat-transfer medium is a solid and there is substantially no net transfer of mass accompanying the transfer of heat.